Arboretum Images 7c

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Palomar College Arboretum Images 7c: Shrubs #3
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Bignonia Family (Bignoniaceae)

Pink dawn (Chitalpa tashkentensis), a bigeneric hybrid between the narrow-leaved desert willow (Chilopsis linearis) and the broad-leaved catalpa tree (Catalpa bignonioides). [Sony T-10]

The orginal cross between Chilopsis linearis and Catalpa bignonioides was made in the early 1960s by F.N. Rusanov of the Uzbek Academy of Sciences Botanical Garden, Tashkent, Uzbekistan (formerly the Republic of Uzbekistan, U.S.S.R). In 1977 an expedition from New York's Cary Arboretum brought cuttings back to the United States. The scientific binomial originated at Rancho Santa Ana Botanical Garden in 1991. Although the showy flowers resemble the parental trees, they are sterile and do not produce seed-bearing capsules. In general overall appearance, this unusual hybrid resembles Chilopsis more than Catalpa.

Athough the parents of this intergeneric hybrid have the same base chromosome number (n=20), the diploid hybrid is sterile. The chromosomes of the two parental species are not homologous resulting in synaptic failure at meiosis I, including abnormal meiotic pairing and abnormal or abortive gamete development. An allotetraploid has two sets of chromosomes from each parental species, a total of four sets. [Note: If all four sets come from the same species it is an autotetraploid.] In the following article, a fertile seed-producing allotetraploid Chitalpa was produced by inducing polyploidy in the diploid hybrid using oryzalin rather than colchine. The resulting allotetraploid has two sets of homologous maternal and paternal chromosomes. Now the original maternal and paternal sets each have a homologous set to pair up with during synapsis:

Olsen, R.T., Ranney, T.G., and Z. Viloria. 2006. "Reproductive Behavior of
Induced Allotetraploid xChitalpa and In Vitro Embryo Culture of Polyploid
Progeny." J. Amer. Soc. Hort. Sci. 131 (6): 716-724.

  How To Make A Fertile Polyploid Hybrid  

Pink dawn (Chitalpa tashkentensis), an intergeneric sterile hybrid between the narrow-leaved desert willow (Chilopsis linearis) and the broad-leaved catalpa tree (Catalpa bignonioides). The leaves are broader than desert willow, but not nearly as broad as the catalpa tree. [Sony T-10]

The catalpa (Catalpa bignonioides) is a large shade tree with heart-shaped leaves and white flowers similar to "pink dawn." In fact, this species is one of the parents of (Chitalpa tashkentensis). The flowers are followed by long, green seed pods (capsules). This tree is sometimes called "Indian bean" but it is not a legume. It is native to the southeastern United States and is commonly planted as a shade tree in areas with hot, humid summers. [Sony H-5]

Desert willow (Chilopsis linearis), a native shrub in desert regions of the southwestern United States. This species was crossed with the catalpa tree (Catalpa bignonioides) of the eastern United States to produce the bigeneric hybrid Chitalpa taskkentensis. The leaves of desert willow are much narrower than the hybrid. [Nikon FM-2]

Desert willow (Chilopsis linearis), a native shrub in sandy desert washes of the southwestern United States. In the Jepson Flora of California (1996) it is listed as var. arcuata. [Sony T-10]

  More Images of the Bignonia Family  
Wind Dispersal in Bignonia Family
Ironwoods in the Bignonia Family
Hybridization & Polyploidy